1. Field of the Invention
The present invention relates to an exhaust structure for suppressing leakage of engine noise or the like from an exhaust port of an engine room in a construction machine such as a hydraulic excavator.
2. Description of the Related Art
In a hydraulic excavator in FIG. 6, an upper rotating body 2 is rotatably mounted on a crawler type lower traveling body 1, and a working attachment 3 is installed to the upper rotating body 2. On a rear part of the upper rotating body 2, is provided an engine room 5 (refer to FIG. 7) which periphery being covered by an engine guard 4.
In the engine room 5 is installed an engine 6, and on one side of the engine 6 are aligned a heat exchanger such as a radiator 7 and a cooling fan 8 in the horizontal direction. On the other side are installed a hydraulic pump 9 and engine related devices (not shown).
An upper surface part of the engine guard 4 is formed by a bonnet 10 protruding upward in a central part in the horizontal direction, and fixed hoods 11 and 12 fixed on the left side and the right side of the bonnet 10.
The bonnet 10 is openably attached for example as a door type (refer to FIG. 6). By the bonnet 10, a maintenance port 13 for maintenance of the engine 6 and the like is opened and closed.
On one of left and right side walls of the engine guard 4 (on the cooling fan 8 side) is provided an intake port 14, and on the other side is provided an exhaust port 15 respectively. By rotation of the cooling fan 8, the outside air is taken from the intake port 14 into the engine room 5.
This cooling air passes around the heat exchanger such as the radiator 7 and the engine and then is exhausted from the exhaust port 15. The heat exchanger, the engine 6 and the like are cooled by this air flow.
At this point, together with the air, engine noise (engine sound and fan sound) is exhausted from the exhaust port 15 being a cause of the noise.
As a countermeasure for the noise, there is a known technique in which an exhaust duct 17 provided with a sound absorbing material 16 is disposed on the inside of the exhaust port 15 along the air flow as shown in FIG. 7 so that the engine noise can be suppressed by a sound absorbing effect of the exhaust duct 17 (Japanese Patent Laid-Open No. 2005-282362, hereinafter also referred to as THE FIRST RELATED ART).
In this case, the exhaust duct 17 is disposed below the fixed hood 11 avoiding the maintenance port 13 so as not to disturb the maintenance.
Japanese Patent Laid-Open Nos. 2004-330854 and Hei9-156384 disclose a technique in which, as shown in FIG. 8 (the same reference numerals applied to the same parts as in FIG. 7), an exhaust port 18 is provided on one of left and right side walls of the bonnet 10, and an exhaust duct 20 provided with a sound absorbing material 19 is attached on the lower surface side of the bonnet 10 facing the exhaust port 18 so that by moving the exhaust duct 20 integrally with the bonnet 10 the maintenance port 13 is opened when the bonnet is opened (hereinafter also referred to as THE SECOND RELATED ART).
In this case, the exhaust duct 20 is disposed in a length range not longer than a port width of the maintenance port 13 so as not to disturb open and close of the bonnet 10.
However, as mentioned above, in a view of ensuring maintenance performance, there are a limitation in which the exhaust duct 17 does not largely interrupt the maintenance port 13 in THE FIRST RELATED ART and a limitation in which a length of the exhaust duct 20 is not longer than the port width of the maintenance port 13 in THE SECOND RELATED ART. As a result, in both cases, it is not possible to have a long duct length. Therefore, a sound absorbing effect by the exhaust ducts 17 and 20 becomes insufficient.
It should be noted that Japanese Patent Laid-Open No. 2005-282362 proposes a technique in which ducts are disposed below both the fixed hood and the bonnet. However, in this case, since two ducts are independently disposed and overlapped as one on the upper side and the other on the lower side, an upper space of the engine room 5 is largely interrupted by the upper duct and the lower duct. Therefore, it is difficult to apply the technique to a small type excavator in which overall height thereof is limited.